Four score and a few years ago, our fathers brought forth upon this continent a new Lincoln® Mark VIII®, conceived in luxury, and dedicated to the proposition that all people were created to drive a comfortable vehicle, clad in leather accommodations and equipped with a properly functioning electronic air temperature control system.

Hey, does that quote sounds vaguely familiar? It should. I thought that since we were discussing a Lincoln® a little Gettysburg Address parallelism would be appropriate.The problematic facts of this technical tip are simple. A faulty or intermittent heater core lockout sensor ground will cause the air conditioning blower to operate on cold engine start up and the Electronic Air Temperature Control (EATC) System is in the "Automatic Mode". The heater core lockout sensor, located in the heater core inlet tube, is also known as the cold engine lockout switch.The repair is to replace the nut that attaches the heater tube support bracket to the back of the engine with a serrated nut. The support tube bracket may not be making a good ground connection through the paint coating on the bracket. Refer to the following procedure for service details.

Procedure:
1. Locate the heater inlet tube and heater core lockout sensor, which is attached to the tube. Refer to the image.
2. Replace the heater tube-attaching nut with a serrated nut.
3. Tighten the nut to 9 to 11 ft. lbs. (12-15 N-m).
4. Verify that a good ground has been made by checking continuity between the sensor base and engine block, or by checking continuity between the heater core inlet tube (which is the lower of the two tubes) and the engine block.